1. Field of the Invention
The present invention relates to a device and method for detecting a position of an edge of a cutting tool.
2. Description of the Prior Art
To accurately detect a position of an edge of a cutting tool, a conventional method is proposed to pick up an image of the edge of the cutting tool by an image pick-up device such as a CCD camera (a camera using charge-coupled devices) with the image enlarged by a microscope, and thereafter to process the image so as to detect the position of the edge of the cutting tool with respect to the microscope or the image pick-up device. Such method is disclosed in PRECISION ENG. (Butterworth & Co., Ltd.), 1989, Oct., Vol. 11, No. 4, Page 231.
In case that a region of 2 mm.times.2 mm is picked up by the CCD camera for picture elements of 1024.times.1024 using the above method, one of the picture elements corresponds to 2 .mu.m.times.2 .mu.m. Generally, in a process of extracting the position of a contour line, etc. by image processing, the accuracy of position of the contour line is degraded by about one figure compared with a resolution of one picture element. Therefore, with the above method, it is difficult to detect the position of the edge of the cutting tool or a configuration of the same by order of micron. To improve the detecting accuracy, it requires to use a microscope of large magnifying rate which is difficult to be applied at a working place.
Further, since the device requires a special light source in addition to such microscope of large magnifying rate, the construction of the device becomes rather complicated and the size of the device becomes larger.